Process for self condensing phosphonitrilic chloroesters and product

ABSTRACT

A NOVEL PROCESS CONSISTING OF REACTING A PHOSPHONITRILLIC CHLORIDE WITH AN ALCOHOL OR ALKOXIDE OF 1 TO 12 CARBON ATOMS TO PRODUCE A PARTIALLY ESTERIFIED PHOSPHONITRILLIC CHLORIDE, REMOVING IMPURITIES FROM THE CHLOROESTER AND HEATING THE ESTER TO FORM A CONDENSED POLYMERIC PHOSPHAZENE WITH P-O-P OXYGEN LINKAGES. THIS NEW CLASS OF POLYMER PHOSPHAZENES, WITH P-O-P OXYGEN LINKAGES, IS UNUSUALLY EFFICACIOUS IN RENDERING RAYON FLAME-RETARDANT.

United States Patent 3,836,608 PROCESS FOR SELF CONDENSING PHOSPHO-NITRILIC CHLOROESTERS AND PRODUCT Borivoj Richard Franko-Filipasic,Morrisville, and Edward Francis Orwoll, Langhorne, Pa., and John FrancisStart, Mercerville, N411, assignors to FMC Corporation, New York, N.Y.No Drawing. Filed Aug. 17, 1972, Ser. No. 281,318 Int. Cl. C07d 105/04;C071? 9/24, 9/26 U.S. Cl. 260926 8 Claims ABSTRACT OF THE DISCLOSURE Anovel process consisting of reacting a phosphonitrilic chloride with analcohol or alkoxide of 1 to 12 carbon atoms to produce a partiallyesterified phosphonitrilic chloride, removing impurities from thechloroester and heating the ester to form a condensed polymericphosphazene with POP oxygen linkages. This new class of polymerphosphazenes, with PO-P oxygen linkages, is unusually eflicacious inrendering rayon flame-retardant.

This invention relates to a process for preparing polymeric phosphazenesby formation of POP oxygen linkages through the condensation of alkylesters of polymeric phosphonitrilic chlorides containing 3 to 10%residual chlorine with elimination of alkyl chloride; the polymericphosphazene composition so obtained; and regenerated cellulose filamentsand filamentary articles which are made permanently flame-retardant byhaving dispersed therein a flame-retardant amount of these substantiallywater-insoluble liquid polymeric phosphazenes.

It is desirable, for many textile purposes to provide cellulose fibersand yarns having greatly decreased flammability. In the manufacture ofrayon by the viscose method, it has been proposed to add variousflame-retardant chemicals to the vicose prior to spinning. This approachpresents many additional problems because of the particular chemistry ofthe viscose process. Accordingly, the flame retardant must be stable andinert with respect to the highly alkaline viscose and also with respectto the acid regeneration bath into which the viscose is extruded. Itmust not be extracted during spinning and processing. Furthermore, theadded material must not interfere with the spinning process, forexample, cause clogging of the spinnerettes.

Rayon has been made permanently flame-retardant by dispersing in therayon a flame-retardant amount of a substantially water-insoluble,liquid phosphonitrilate polymer as disclosed by Godfrey in US. Pats.Nos. 3,455,713, 3,505,087 and 3,532,526, respectively, issued July 15,1969, Apr. 7, 1970, and Oct. 6, 1970. Although the Godfrey compositionsdo not seriously degrade rayon fiber properties, it is always desirableto have more effective flame retardants allowing attainment of adequateflame retardance at a lower additive level with a consequent loweredimpairment of physical properties of the rayon fibers and a decrease incost.

In accordance with the present invention there is provided a novelprocess for producing novel liquid polymeric phosphazenes, which whendispersed in regenerated cellulose make the regenerated cellulose highlyflame resistant. The phosphazene units are randomly linked together byoxygen bridges connecting phosphorus atoms of neighboring phosphazeneunits.

The novel process consists of partially esterifying a phosphonitrilicchloride which may consist of 100% linear polymers or of 100% cyclicpolymers or any mixture of linear and cyclic polymers, with a metalalkoxide, or an alcohol in the presence of an acid acceptor, in whichthe alkyl portion of the alcohol or alkoxide contains 1 to 12 ice carbonatoms and the esterification is continued to a point where thechloroester contains 1% to 15% and preferably 3 to 10% by weightunreacted chlorine based on the weight of the chloroester. Impuritiesare removed from the chloroester filtering or washing, thereby removingwater soluble materials, generally salts and other byproduct impurities.The chloroester is heated to condense it into a polymer of increasedmolecular weight, by heating at a temperature between about C. to about250 C., preferably, C. to 220 C., removing the alkyl chloride andleaving behind the condensed polymeric product. The condensedphosphazenes of this invention are liquids, generally of pumpableviscosity. Very high viscosity materials can be diluted with solvents tofacilitate incorporating the phosphazene into rayon.

The reaction of a phosphonitrilic chloride polymer with an alkoxide, oralcohol in the presence of an acid acceptor, is conventionally done byadding the phosphonitrilic chloride to a stirred slurry of the alkoxide.A stoichiometric insufficiency of the alkoxide is used to produce achloroester containing 1 to 15% residual chloride. The esterification isconveniently done in a solvent or diluent and the esterificationreaction is generally conducted at the reflux temperature of the solventand/or diluent selected as the reaction medium.

Ordinarily, phosphonitrilic chloride is added to a slurry ofinsufiicient alkoxide, such as propoxide, and the esterification iscompleted in the usual way. The reaction proceeds in a manner so thatfirst phosphonitrilic chloride molecules which react are completelyesterified, thus, producing a mixture of completely esterified oressentially completely esterified material mixed in with unreactedpolymeric phosphonitrilic chloride. However, a reverse addition process,in which the alkoxide is added to a suitable liquid phosphonitrilicchloride produces a particularly efiicacious product. The reverseaddition process produces, more chloroester and little or no unreactedphosphonitrilic chloride is left unreacted.

The condensation of the chloroester is conveniently done by heatingunder vacuum to facilitate removal of by-product alkyl halides and anyretained solvent or diluent utilized in the esterification reaction.Condensation of the chloroester under vacuum takes less time, there isless color build-up in the final product and residual solvent and otherlow boiling impurities remaining in the reaction mixture are easilyremoved.

In accordance with the invention a phosphonitrilic chloride polymer ofthe general formula:

hail

T at.

where n is at least 3, is reacted with an alcohol or alkoxide having 1to 12 carbon atoms to produce a partially chlorinated ester which may becyclic or linear, which for convenience is represented by the generalstructure:

carbon atoms; R may also have substituent groups including halogens,ether or amino groups. Some of the X and Y substituents remain halogensfrom the phosphonitrilic halide polymer from which the ester wasderived. Usually, the halogen is chlorine.

For convenience, the formulation:

is used to denote both cyclic and linear analogs where X and Y are asdefined above. It is understood that the linear analogs are morecorrectly formulated as:

where Q and Z represent end capping groups and X and Y are as definedabove. In the linear oligomers n is 2 or more. For instance, Z may be ORwhile Q may be end caps, R having the meaning ascribed above. Similarly,for linear phosphonitrilic chlorides,

T at

Z may be Cl while Q may be -PCl PCl or PCl C1 or While n is generally atleast 3 for linear as well as for cyclic analogs, some small proportionof the linear fraction may contain components wherein n is less than 3.

The chloroester is condensed, with elimination of alkyl halide. In asimple example of the invention self condensation of a trimericchloroester results in mixtures of products one member can berepresented by the general structure:

in which R is as defined above. The actual compositions are morefrequently mixtures of linear and cyclic materials which includetetramers and higher cyclic polymers. Thermalalkoxyphosphazene-oxophosphazene rearrangement is known to obtain at thetemperatures utilized in the present process. Some of the ester presentin the products of the present process may be of the latter structure.The rearrangement is discussed by Shaw, R. A., Records of ChemicalProgress, Vol. 28, 1967, pp. 243- 258, The Phosphazenes.

The reaction between the alkyl and phosphorus halide groups withelimination of alkyl halide can proceed with or without solvent. Therelative ratio between alkyl and phosphorus halide groups can varywidely because of the many reactant options available. In practice,reactant ratios are limited since preferred compositions retain 3 to 10%chlorine.

The reaction between the alkyl and halide groups proceeds at about 100to about 250 C., with considerable variability in the reactivity of thehalide component. The

4 reaction may be conducted batchwise or continuously. Reaction ratesare slow at the lower end of the temperature range; discoloration andcompetitive decomposition reactions tend to ensue at the upper end. Thepreferred temperature range is, therefore, to 220 C.

Thermal dependence of the rate of reaction to eliminate alkyl chloridewas observed in the examples for the temperature range of 220 C., whichexamples utilized cyclic phosphonitrilic chloride to form thechloroesters. When a phosphonitrilic chloride containing 23% noncyclicmaterials, linear phosphonitrilic chloride, was used to prepare thechloroester, enhancement of reaction rate in the thermal condensationreaction was observed. Examination of examples 1 to 6 shows that thereaction appears to have occurred in less time than the expected timeinterval when using higher temperatures indicating an acceleratedreaction rate due to including non-cyclic phosphonitrilic chloride inthe preparation of the chloroesters. Thus, it is preferred to use asstarting material polymeric phosphonitrilic chlorides containing about10% to about 80% linear polymers, the balance of the starting materialbeing cyclic polymers.

As the reaction between alkyl and halide groups proceeds, low boilingalkyl chloride is eliminated. Atmospheric or reduced pressure in therange of 5 to 760 mm of mercury pressure is preferred to promote removalof the alkyl chloride. Subatmospheric pressures are preferred as theylimit discoloration of the product.

Depending upon choice of reactants, the condensation time variesgenerally from a few minutes, about 5 to 10, to 12 hours at thepreferred temperature range. Condensation proceeds more rapidly athigher temperatures along with some discoloration. Optimumtime-temperature conditions must be found for each chloroestercomposition. Time may be further extended if a particularly low halogencontent or a higher visco ity is desired.

The reaction may be run in inert solvents (diluents) preferably chosento reflux at the desired reaction temperature, for example, octane orchlorobenzene. A solvent from which by-product alkyl chloride is easilyseparated is desired. When a low-boiling solvent is chosen, pressuresuflicient to achieve a desired reaction temperature is used. When thereaction is run Without solvent, it is expedient to pass a slow streamof inert gas, such as N through the reaction mixture to sweep out alkylchloride. The extent of reaction can be monitored by measurement ofalkyl chloride evolved or analysis for residual chloride.

No unusual equipment is required. A standard reactor equipped withdevices for metering, agitating, heating, cooling, refluxing anddistilling is applicable.

Although the reaction proceeds without catalyst, the reaction rate ismaterially increased by the presence of a catalyst. The use of acatalyst, such as copper, reduces time and temperature required, anddecreases the extent of discoloration and decomposition reactions.

The amount of flame retardant of this invention dis persed inregenerated cellulose (rayon) depends on pro viding a proper balancebetween flame retardancy and fiber properties. Useful amounts of theflame retardant can be varied from 1% to about 25% and preferably 2% to18% based on the Weight of the filament.

The flame-retardant compounds of this invention are incorporated intoregenerated cellulose filaments by any of the known methods forpreparation of such filaments. While the viscose method is preferred,the flameretardant compounds can be incorporated in cellulosicsolutions, spun into filaments and the cellulose regenerated. Thus, thecuprammonium method and the desterification of a cellulose ester methodcan be utilized to prepare regenerated cellulose filaments having theflame-retardant compounds incoroprated therein.

One embodiment of this invention comprises incorporating theabove-described liquid polymeric phosphazene in a viscose solution andspinning the viscose in the shape EXAMPLE I A suspension of sodiumpropoxide was formed in 5.2 liters of mixed xylenes by charging 1140 mlof n-propanel to 308 g. (13.4 moles) of agitated molten sodium at 110 to115 C. The reaction was completed by stirring at reflux for anadditional one half hour. A chloroester was prepared by charging a 19.3%stoichiometric excess '(928 g., 8 moles) of cyclic phosphonitrilicchloride in chlorobenzene solvent to the propoxide suspension at refluxtemperatures. The chloroester formed in three hours. The chloroester wasisolated by water-washing the cooled reaction mixture and concentratingthe organic layer in vacuo (85, 16 torr). The chloroester was thenheated in a rotating flask at 200 C., torr for 12 minutes. Analyses ofprecursor chloroesters (A) and thermally treated product (B) aretabulated.

Analysis (A) (B) Carbon 38. 03 37. 85 Hydrogen 7. 62 7. 22 Nitrogen 8.49 10. 12 Phosphor 20. 90 22. 96 C ine 6. 44 1. 98 Molecular weight---630 1020 Acid number 6. 7 14 Viscosity at 25 0., cs- 220 2, 500Refractive index at 25 C 1. 4755 EMMPLE II Example I was repeated,except that thermal treatment of chloroester was carried out at 170-180C., 19 torr for 55 minutes. Analyses of ester before (A) and after (B)thermal treatment are tabulated.

Analysis (A) (B) Carb 97 38. 02 Hydrogen 7. 61 7. 33 Nitrogen 8. 61 9.60 Phosphor 73 21. 31 Chlorine 6. 34 2. 45 Molecular weight. 640 1, 210Acid number 3. 6 8. 3 Refractive index at 23 0.- 1. 4676 1 4745Viscosity at 25 0., cs 6, 800

EXAMPLE III Example I was repeated except that the thermal treatment wascarried out at 150, 16 torr, for /2 hours. Analysis of the productfollows. Values in parenthesis are for untreated chloroester.

EXAMPLE IV Example I was repeated except that the thermal treatment wascarried out at 220 C., torr, for 8 minutes. Analysis of the productfollows. Values in parenthesis are for untreated chloroester.

Analysis (A) (B) Carbon 38. 46 (40. 07) Hydrogen. 7. 39 (7. 32) Nltrogen 9. 86 (9. 06) Phosphorus 22. (20. 69) Chlorlne 0. 55 (3. 54)Molecular weight. 923 (612) Acid number 13. 4 (14. 7) Viscosity at 25,cs.- 6993 (44. 2) Refractive index at 21 1. 4748 (1. 46 5) Thephosphorus-containing product was evaluated for its flame-retardanteffect in rayon yarn produced from a filament-forming viscose comprising8.6 wt. percent cellulose, 6.2 wt. percent sodium hydroxide and 33.0%carbon disulfide, based on the weight of the cellulose, and having aviscosity at spinning of 6000 centipoises at 18 C. Thephosphorus-containing flame-retardant compound was injected into theviscose stream at the desired rate based on the weight of the cellulosein the viscose and the viscose mixture passed through a high shearblender. This provided a viscose having the flame retardant dispersedtherein as fine liquid particles of from 1 to 10 microns in size.

The viscose was spun into a conventional aqueous acid spin bathcomprising 9.8 wt. percent sulfuric acid, 3.0 wt. percent sulfate and17.5 wt. percent sodium sulfate at a bath temperature of 50 C. The yarnwas wet stretched about 35% of its original length. Yarns having adenier of 240 and 40 filaments were processed by passing them through aseries of baths including water wash, desulfurization, bleach, bleachacid, antichlor, and soft finish bath. The yarns were dried, transferredto packages, and finally knit into circular knit fabrics. Theregenerated cellulose yarns prepared in this manner were made up ofindividual filaments having fine liquid flame-retardant particles lockedin the cellulose matrix. The fabrics retained 15% by weight of thephosphazene and the fabric was found to be flame resistant.

EXAMPLE V The preparation of Example I was modified by using a polymericphosphonitrilic chloride that contained 23% hexane insoluble(non-cyclic) chlorophosphazenes the balance being cyclic material. Thethermal treatment Was carried out at 150 C., 22 torr, for 7-1 2 hours.Analysis of the product follows. Values in parenthesis are for untreatedchloroester.

Analysis (A) (B) Carbon 39. 23 (40. 80) Hydrogen. 7. 83 (8. 15) Nitrogen 9. 79 (9. 34) Phosphorus. 21. 53 (19. 75) Chlorine 1. 28 (4. 89)Molecular weigh 980 (683) Acld number. 6. 7 (4. 6) Viscosity at 25, 4,000 1 (320) Refractive index at 30 1. 4692 I (1. 4626) EXAMPLE VI Thepreparation of Example I was modified by using a polymericphosphonitrilic chloride that contained 64.2% hexane insoluble(non-cyclic) chlorosphosphazenes. The thermal treatment was carried outat -150, 22 torr, for 65 minutes. Analysis of the product follows.Values in parenthesis are for untreated chloroester.

7 What is claimed is:

l 1. A process for producing a liquid polymeric phosphazene comprising(1) reacting a phosphonitrilic chloride With a metallic alkoxide or analcohol in the presence of an acid acceptor, the alkyl portion of thealcohol or alkoxide being a radical of 1 to 12 carbon atoms, to producea chlorinated phosphazene ester containing 1 to 15% unreacted chlorineby weight based on the weight of the chloroester, (2) heating thechloroester at a temperature of about 130 C. to about 220 C. to producea condensed polymeric phosphazene ester of increased molecular weight.

2. The process of claim 1 in which the phosphonitrilic chloride is amixture of linear polymers.

3. The process of claim 1 in which the phosphonitrilic chloride is amixture of cyclic polymers.

4. The process of claim 1 in which the phosphonitrilic chloride is amixture of cyclic and linear polymers.

5. The process of claim 1 in which the chloroester is heated undervacuum to facilitate removal of by-product alkyl chloride.

6. The process of claim 1 in which the phosphonitrilic chloride is addedto the alkoxide to'producethe chloroester. "f 7. The process of claim 1in which the all roxide is added to the phosphonitrilic chloride toproduce the chloroester; 8. The product of the process of claim 1. V

References Cited UNITED STATES PATENTS 7 3,419,504 12/1968 Klender260927 N OTHER REFERENCES Herring et a1. Inorganic Chemistry Vol.4 ('7),pp. 1012-6 (1965).

ANTON H. SUTTO, Primary Examiner U.S. Cl. X.R.

106l5 PP, 168; 260927 N, 973, 978

